Steps towards a capacitance standard based on single-electron counting at PTB

TL;DR

This paper discusses the development of a quantum-based capacitance standard using single-electron counting and Josephson voltage standards, with recent progress on the experimental setup and electron transfer mechanisms.

Contribution

It introduces modifications to the single-electron circuit to enable precise capacitor charging with an r-pump for quantum capacitance measurement.

Findings

Progress in setting up the single-electron counting experiment

Characterization of single-electron tunneling elements

Circuit modifications for improved electron transfer

Abstract

A capacitance standard based on the definition of capacitance C = Ne/U is realized when a capacitor is charged with a known number N of electrons (e is the elementary charge) and the voltage U across the capacitor is measured. If U is measured by means of a Josephson voltage standard, C is solely determined by quantum numbers and fundamental constants. Presently, PTB is setting up this experiment using a special type of single-electron pump, the so-called r-pump, for transferring electrons one by one onto a cryogenic vacuum capacitor with the decadic capacitance C = 1 pF. We report on the progress in the setup with emphasis on the characterization of the single-electron tunneling elements. We describe the modifications of the single-electron circuit that are necessary to implement the capacitor charging experiment by using a four- or five-junction r-pump.